This invention relates to devices for compensating for wear in a disc brake assembly and is particularly, but not exclusively, concerned with such devices for use in aeronautics.
Aircraft with wheeled undercarriages are generally equipped with mechanical brakes, normally of the disc type or multiple disc type, which act directly upon the wheels and are adapted to absorb both the energy produced during normal landing and also the energy of much greater magnitude which results from emergency braking in exceptional conditions.
In both these cases a very high braking capacity is required which may act for only a few seconds, but which should act in a continuous and efficient manner. It is extremely important, in view of the speed of the aircraft when landing, that the operation of the brake in response to the command of the pilot should be as rapid as possible and should remain substantially constant in spite of wear in the brake linings.
As a consequence of the very high capacity demanded, aircraft brakes are usually composed of a plurality of braking discs connected to the wheels for rotation therewith and disposed between friction linings connected to standard hydraulically operated pincers or jaws equipped with pistons on one side only.
Thus, for example, a brake with two discs requires four linings which grip the discs between them during braking and are subject to wear and to considerable heating.
Both the wear and the heat result in braking conditions which never remain the same with time and, in particular, the wear of the linings leads to differences of the order of several millimeters, at times even greater than ten millimeters, in the total thickness of the linings plus discs, as between the condition when the linings are new and the condition when the linings are worn, but nevertheless are still operational. In these cases the stroke that must be travelled by the pressure applying piston in order to ensure that the linings grip the discs must be such as to accommodate the wear in the linings in addition to the normal thermal expansions and the elastic movements of the assembly. Since the last two causes cannot be eliminated, the technical problem which arises consists of so arranging the pressure applying piston as to guarantee, at rest, only a minimum of play between the linings and the discs, such as to leave the discs and the wheel free while nevertheless taking account of the temperature to which the brake assembly is subjected at the end of braking, which temperature may indeed be quite high depending upon the use.
These technical problems which to some extent are in opposition are solved by a device according to the present invention, in a simple and effective manner and in such a way as to take account, not only of the wear of the linings, but also of the variations in temperature, expansion and elastic deformation to which the brakes are subjected.